Many listings on Amazon, AliExpress, eBay and in other places incorrectly state that the CCS811 is a Carbon Monoxide (CO) sensor. It is not. It reports eTVOC (equivalent Total Volatile Organic Compounds) and eCO2 (equivalent Carbon Dioxide). The CCS811 is not capable of measuring Carbon Monoxide and any listing or description of it that says it does is simply incorrect. It also doesn’t truly measure CO2, but that’s a story for another day.